232 



RADIOACTIVITY AND POTASSIUM 



due to its radioactivity, we should have to conclude that cesium has 

 the same degree of radioactivity as potassium which is contrary to 

 the facts known at present. Development with CsCl is possibly 

 slower than with KCl, and the development does not go so far as in 



TABLE II. 



Concentration of Cesium Needed for Development. 



the case of KCl probably on account of the greater toxicity of cesium 

 which in rather low concentrations kills the larvae. 



D. Thorium Chloride Experiments. — It seemed important to deter- 

 mine whether or not potassium could be replaced by a radioactive 

 element like thorium. Zwaardemaker found that in winter a solu- 



